The present invention relates to a fabrication machine of high performance optical fiber using a melt spinning method, and more particularly to a fabrication machine for reliably spinning high performance sea island optical fiber composed of at least two kinds of fibers into a predetermined shape.
Conventionally, a coloring structural body in which color is changed depending on a direction to be seen and which is elegant and high-grade feeling and has a color tone of higher saturation, has been required from users' multi-taste and high rank orientation. This requirement cannot be achieved by only coloring matters such as dyes, pigments and the like but by a structural body colored by reflection, interference, diffraction or scattering of light, or a combination of this coloring function and such coloring matters, and deeply and vividly coloring structural bodies have been energetically researched and developed.
Many proposals have so far been done, for example, a composite fiber constituted by at least two resins with different optical refractive indexes, having pearly luster (Japanese Patent Publication Gazette No. 43-14185, Japanese Patent Laid Open Gazette No. 1-139803); a coloring material having a sandwich construction composed of one molecular orientation anisotropic film and two polarizing films sandwiching the film between (Proceedings of the Textile Machinery Society of Japan, Vol. 42, No. 2, p. 55 and No. 10, p. 60, 1989); a coloring structural body utilizing the coloring of Morphinae butterfly from South America, which is famous for which the color tone is changed depending on a direction to be seen and has vivid color tone efficiency (Japanese Patent Laid Open Gazette No. Sho 59-228042, Japanese Patent Publication Gazette No. 60-24847, Japanese Patent Publication No. Sho 63-64535); and a structural body emitting an interference color by forming fine slits having a fixed width on fiber surface (Japanese Patent Laid Open Gazette No. 62-170510, Japanese Patent Laid Open Gazette No. 63-120642).
However, for these coloring structural bodies, various problems arise for their practical uses, for example, it is difficult to control conditions for attaining a predetermined function, and a spinneret suitable for keeping a composite fiber having a complicated shape cannot be obtained.
The present applicants have developed coloring optical fiber having a vivid color taste changeable in a direction to be seen and a reflection interference function without a change with the elapse of time (Japanese Patent Laid Open Gazette No. 6-17349). This optical fiber has a cross section of a sea island type, as shown in FIG. 1a, and comprises a core 1 extending in a longitudinal direction, six pairs of wing portions 2 connected to, and arranged with slits therebetween on, both the sides of the core 1, the core 1 and the wing portions 2 constituting an island part 3, and a sea part 4 filling up the periphery of the island parts 3 and the slits between the wing portions 2. The island part 3 and the sea part 4 of the sea island type optical fiber are made different in their optical refractive indexes to provide an optical fiber having a vivid color and a color taste changeable in a direction to be seen. Usually, the sea part of the optical fiber is dissolved and only the island part is used as the optical fiber, as shown in FIG. 1b.
In order to manifest the optical function of this optical fiber, it is necessary to ensure the foregoing shape and dimensions. The above described optical fiber is constituted by the wing portions having a thickness of approximately 0.01 to 0.1 mm, and it is the most essential point in the steps from the polymer dissolution to the fiber preparation to certainly separate the slits between the adjacent wind portions 2 to maintain the predetermined shape. However, when spinning the molten polymer, the spacing between the adjacent wing portions 2 is narrow and a mutual contact or fusion is often caused in the wing portions 2.
In order to solve this drawback, the present applicant has developed a spinneret for use in fabricating an optical fiber, as shown in FIGS. 2 and 3 (Japanese Patent Application No. 7-28519 and Japanese Patent Application No. 7-28521). FIG. 2 is a perspective view, partly in section, seen from the lower side, of a spinneret for fabricating an optical fiber, omitting a lower funnel-shaped nozzle portion and FIG. 3 is a longitudinal cross section of the spinneret shown in FIG. 2, including the lower nozzle portion.
In FIGS. 2 and 3, the spinneret 5 includes a ring-shaped spinning head 8 having polymer inlets 6 and 7 for the island and sea parts 3 and 4, a bottom 9, and a concavo-convex-shaped partition wall 10 for a flow path control of the island part 3, mounted on the bottom 9, so as to surround the space corresponding to the island part 3 in its upper half. The spinneret 5 also includes a spinning seat 12 having a funnel-shaped spinning nozzle 11 in its center under the spinning head 8 in its lower half.
In FIG. 3, as shown by arrows, a polymer for the island part 3 is introduced from the polymer inlet 6 into the inside of the partition wall 10 and another polymer for the sea part 4 from the polymer inlet 7 into the peripheral space of the partition wall 10, resulting in forming the shapes corresponding to the island part 3 and the sea part 4 of the optical fiber, as shown in FIG. 1a, in conformity to the internal and external shapes of the partition wall 10. The two polymers contact their conforming surfaces to each other to integrate, while moving down in the spinning nozzle 11, to spin into a sea island type optical fiber, as shown in FIG. 1a.
In this spinning method, when the sea part polymer is introduced form the polymer inlet 7 into the space or slits 13 of the adjacent external projection wings of the partition wall 10 shown in FIG. 2, the sea part polymer enters the slits sufficiently between the adjacent wing portions 2 and the spinning is carried out as it is. As a result, the adjacent wind portions 2 are spun into the predetermined shape without a welding to produce an optical fiber having the foregoing desired characteristics.
However, as described above, this optical fiber is of a very fine size, and the slits between the adjacent wing portions 2 are finer. As shown by the arrows in FIG. 3, two flow paths of the sea part polymer are formed in the spinneret 5 of the optical fiber, that is, the flow path passing through the slits 13 and the flow path not passing through the slits 13. When the polymer passes through the slits 13, the resistance against the polymer flow is rather high. Accordingly, almost all the sea part polymer comes into the funnel-shaped spinning nozzle 11 without passing through the slits 13, and the spinning is liable to be performed in the state that a sufficient amount of the sea part polymer is not supplied within the slits between the wings 2 shown in FIG. 1a.
When the height of the projected partition wall 10 is high, the chance that the polymer enters the slits 13 becomes large, the amount of the polymer passing through the slits 13 increases. However, concerning the actual aspect of processing, it is pretty difficult to carry out a machining of such fine partition wall 10. In particular, when the height of the partition wall 10 increases, the machining becomes more difficult. Accordingly, it is demanded that the height of the partition wall 10 is restricted to be low, but in such a low partition wall, the amount of the polymer passing through the slits 13 is apt to further diminish.
In the optical fiber spun in this manner, the adjacent wing portions 2 tend to contact to each other or to be fusible, and the optical fiber often fails to have the required optical characteristics. This is a main cause to prevent from its practical use.
As described above, the optical fiber is spun as a fiber having very fine concave-convex surfaces. In such an optical fiber, in order to manifest a reflection interference function, assuming that a thickness and an optical refractive index of wing portions are db and nb, respectively, and a thickness and an optical refractive index of air space between the wing portions are da and na, respectively, and that a reflection wavelength of light is .lambda. in a case of a vertical incidence of light, the following formula is given: EQU .lambda.=2(nada+nbdb) (1)
Particularly, when both are equal in their optical thickness, that is, nada=nbdb, the optical function is maximum. The optical thickness is defined as a "geometric thickness (simple `thickness` usually used).times.optical refractive index" of each of the wing portions and the air space between the wing portions.
Accordingly, a thickness of one wing portion is a value which is obtained by dividing the reflection wavelength .lambda. (coloring wavelength in a visible light area) by 4 times of the optical refractive index of the island part fiber. For example, in the case of blue color, when the island part is formed by a PET (polyethylene terephthalate) polymer with respect to a blue color wavelength=0.47 mm, this value is divided by 4 times of the optical refractive index 1.56 of the PET polymer to obtain the thickness approximately 0.08 mm of the wing portions. It has been found that, when the optical fiber is provided with at least 8 slices of fine wings, the coloring effect is raised. Even when the spacing of the air space between the wind portions is determined to 0.12 mm, the thickness of one optical fiber is 8.times.0.08 mm+7.times.0.12 mm=1.48 mm which is still very fine. On the other hand, When optical fibers having different optical thicknesses are produced by using the same spinneret, the discharge amount ratio between the sea part polymer and the island part polymer to be supplied into the spinning nozzle 11 shown in FIG. 3 is controlled. When the amount of the sea part polymer to be supplied into the spinning nozzle 11 is more than that of the island part polymer, the amount of the sea part polymer occupied in the cross section of the optical fiber after the spinning is much and an optical fiber having a small size island part is obtained, as shown in FIG. 1c, and by dissolving out the sea part, a small size optical fiber having the same shape as shown in FIG. 1b can be prepared.
In such a small size optical fiber, if a further sufficient amount of sea part polymer is not supplied into the slits between the wing portions, an optical fiber is not spun into the predetermined shape and an optical fiber having the further desired optical characteristics cannot be provided.